There has been known a fixing device provided in a printer or a copying machine. Japanese Patent Application Publication No. 2007-310377 discloses a fixing device including a hollow cylindrical rotary body, a heat member such as a tubular heater positioned at an inner space of the rotary body and extending in an axial direction of the rotary body (i.e., direction of a rotational axis of the rotary body), a first insulator, a second insulator and a support frame. The first insulator and the second insulator are made from glass and hold one end portion and another end portion of the heat member in the axial direction, respectively. The support frame includes a first support wall supporting the first insulator and in contact with one side surface of the first insulator in the axial direction, and a second support wall supporting the second insulator and in contact with another side surface of the second insulator in the axial direction. With this structure, the heat member is supported so as not to move in the axial direction. That is, movement of the heat member in the axial direction is restricted by the support frame.